Belt for continuously variable transmission

ABSTRACT

When a tangential friction force received by a pulley abutment surface 37 of a metal element 32 from a pulley is represented by FV; a radial distance from a point 45 of action of the tangential friction force to a rocking edge 40 located radially outside the friction force-acting point 45 is represented by L; a radially inward load received by the metal element 32 from a metal ring assembly 31 is represented by FL; and a thickness of the metal element 32 is represented by t, the radial distance L and the thickness t of the metal element are determined, so that a relation, L/t&lt;=FL/2FV is established. Thus, even if a moment FVxL is applied to the metal element 32 by the tangential friction force FV, the moment FVxL can be canceled by a moment FLx(t/2) generated by a load FL for urging an edge a of a ring slot 35 by the metal ring assembly 31, thereby preventing the inclination of the metal element 32 to enhance the durability of the metal ring assembly.

FIELD OF THE INVENTION

The present invention relates to a belt for a continuously variabletransmission comprising a large number of metal elements supported onmetal ring assemblies each of which is comprised of a plurality ofendless metal rings laminated one on another.

BACKGROUND ART

As shown in FIG. 3, if a metal element 32 supported with each of ringslots 35 thereof fitted over a metal ring assembly 31 is inclined withrespect to the metal ring assembly 31, edges a and b of the ring slot 35abut against an inner periphery of the metal ring assembly 31. For thisreason, there is a problem that a large stress is produced in suchabutment portion to exert an adverse influence to the durability of themetal ring assembly 31. The inclination (pitching) of the metal element32 is caused when a friction force by an urging force acting between themetal elements cannot resist against an angular moment by a tangentialfriction force received by the metal element 32 on its surface incontact with a pulley. This tendency is particularly significant in anoutlet portion of a driven pulley. The reason will be described below.

It is known that as shown in FIG. 4A, the tangential friction force FVreceived by the metal element 32 (see FIG. 3) from a drive pulley 6 or adriven pulley 11 is larger in the outlet portion of the pulley 6 or 11,and the value of the friction force FV reaches four times a valuegenerated when the tangential friction force FV is averagely distributedover the entire area of the pulley 6 or 11 around which the metalelement is wound, for the reason that the pulley 6 or 11 is deformed tocause a concentration of the axial thrust. As can be seen from FIG. 3,the tangential friction force FV acts on the metal element 32 so as tofall the metal element 32 in a counterclockwise direction about thecenter 44 of swinging movement.

Furthermore, as shown in FIG. 4B, the urging force E acting between themetal elements 32 to inhibit the inclination of the metal elements 32has a large value in the outlet portion of the drive pulley 6, but is 0(zero) in the outlet portion of the driven pulley 11. As can be seenfrom FIG. 3, radial friction forces E₁ are applied to front and rearsurfaces of the metal element 32 by the urging force E so as to fall themetal element 32 in a clockwise direction about the center 44 ofswinging movement, namely, to oppose a counterclockwise moment generatedby the tangential friction force FV. Therefore, the metal element 32 isliable to be inclined to the largest extent in a position in which thetangential friction force FV acting the metal element 32 to incline themetal element 32 is the maximum and the urging force E inhibiting theinclination of the metal element 32 is 0 (zero), i.e., in the outletportion of the driven pulley 11.

A belt for a continuously variable transmission has been proposed inJapanese Patent Application Laid-open No.6-10993, in which a projectionis formed on a saddle surface of a ring slot in a metal element (on aface against which an inner periphery of a metal ring assembly abuts),the projection being offset forwards in a direction of movement of themetal element from a thickness-wise central portion of the metalelement, so that a moment generated by the tangential friction force iscountervailed by a load for urging the projection by the metal ringassembly, thereby to prevent the inclination of the metal element.

However, if the projection is formed on the saddle surface of the ringslot in the metal element, it is difficult to form the metal elementonly by pressing. This causes not only a problem that it is necessary tocarry out the machining or cutting after the pressing to bring about anincrease in processing cost, but also a problem that a local compressivestress is generated in the inner periphery of the metal ring assemblyabutting against the projection on the saddle surface, this causing theamplitude of a stress inside the innermost metal ring to increase tothereby reduce the durability. Further, in the art disclosed in JapanesePatent Application Laid-open No.6-10993, it is difficult to effectivelyprevent a moment acting so as to fall the metal element in the advancingdirection.

DISCLOSURE OF THE INVENTION

The present invention has been accomplished with the above circumstancesin view, and it is an object of the present invention to ensure that theinclination of the metal element is prevented without increasing theprocessing cost of the metal element to enhance the durability of themetal ring assembly.

To achieve the above object, according to the present invention, thereis provided a belt for a continuously variable transmission, comprisingmetal ring assemblies each of which is comprised of a plurality ofendless metal rings laminated one on another, and a large number ofmetal elements supported along the metal ring assemblies, the belt beingwound around a drive pulley and a driven pulley to transmit a drivingforce, the metal element comprising ring slots into which the metal ringassemblies are fitted, pulley abutment surfaces provided radially insidethe ring slots to abut against the drive pulley and the driven pulley, arocking edge which is provided at a radially inner end of a main surfacefor transmitting an urging force between said metal elements, and whichserves as a fulcrum for the pitching of the metal elements,characterized in that a relation, L/t≦FL/2FV is established, wherein FVrepresents a tangential friction force received by the pulley abutmentsurface from the drive pulley and the driven pulley; L represents aradial distance from a point of action of the tangential friction forceto the rocking edge located radially outside the friction force-actingpoint; FL represents a radially inward load received by the metalelement from the metal ring assemblies; and t represents a thickness ofthe metal element.

With the above arrangement, when the tangential friction force receivedby the pulley abutment surface from the drive pulley and the drivenpulley is represented by FV; the radial distance from the point ofaction of the tangential friction force to the rocking edge locatedradially outside the friction force-acting point is represented by L;the radially inward load received by the metal element from the metalring assembly is represented by FL; and the thickness of the metalelement is represented by t, the relation, L/t≦FL/2FV is established.Therefore, even if a moment is produced to fall the metal elementforwards by the backward tangential friction force acting on the pulleyabutment surface of the metal element in the outlet of the drivenpulley, a load for urging the rear edge of the ring slot radiallyinwards by the metal ring assembly cancels the moment to prevent theinclination of the metal element. As a result, the angle formed by themetal ring assembly and the ring slot of the metal element is maintainedat a right angle and hence, it is possible to prevent a local load frombeing applied to the inner periphery of the metal ring assembly by theedge of the ring slot and to inhibit the increase in amplitude of astress inside the innermost metal ring, thereby enhancing the durabilityof the metal ring assembly. Moreover, the pulley abutment surface of themetal element can be accurately brought into surface contact with thepulley to avoid the generation of an abnormal wearing. Further, theouter periphery of the metal ring assembly is prevented from interferingwith the metal element and hence, it is possible to inhibit the increasein amplitude of the stress in the outermost metal ring and to preventthe local load inside the innermost metal ring from being increased by areaction force from the interference. In addition, it is unnecessary toprovide a special shape in a thickness-wise direction to the saddlesurface of the ring slot in the metal element, against which the metalring belt assembly abuts and hence, there is not a possibility that theprocessing cost for the metal element may be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 7B show embodiments of the present invention. FIG. 1 is askeleton illustration of a power transmitting system of a vehicle havinga continuously variable transmission mounted thereon; FIG. 2 is apartial perspective view of a metal belt; FIG. 3 is an enlarged viewtaken in the direction of an arrow 3 in FIG. 2; FIG. 4A is a diagramshowing the distribution of a tangential friction force on a metalelement; FIG. 4B is a diagram showing the distribution of an urgingforce acting between the metal elements; FIG. 5 is a graph showing aregion in which the inclination of the metal element is not produced;FIGS. 6A and 6B are diagrams showing the shape of the metal elementaccording to an embodiment of the present invention; FIGS. 7A and 7B arediagrams showing the shape of the metal element according to the otherembodiment of the present invention; and FIGS. 8A and 8B are diagramsshowing the shape of a conventional metal element.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will now be described withreference to the accompanying drawings.

FIG. 1 shows the skeleton structure of a metal belt-type continuouslyvariable transmission T mounted on an automobile. An input shaft 3 isconnected to a crankshaft 1 of an engine E through a damper 2 and alsoconnected to a drive shaft 5 of the metal belt-type continuouslyvariable transmission T through a starting clutch 4. A drive pulley 6 ismounted on the drive shaft 5 and includes a stationary pulley half 7secured to the drive shaft 5, and a movable pulley half 8 which ismovable toward and away from the stationary pulley half 7. The movablepulley half 8 is biased toward the stationary pulley half 7 by ahydraulic pressure applied to an oil chamber 9.

A driven pulley 11 mounted on a driven shaft 10 disposed in parallel tothe drive shaft 5 includes a stationary pulley half 12 secured to thedriven shaft 10, and a movable pulley half 13 which is movable towardand away from the stationary pulley half 12. The movable pulley half 13is biased toward the stationary pulley half 12 by a hydraulic pressureapplied to an oil chamber 14. A metal belt 15 (see FIG. 2) comprising alarge number of metal elements 32 supported on a pair of left and rightmetal ring assemblies 31, 31 is wound around the drive pulley 6 and thedriven pulley 11. Each of the metal ring assemblies 31 comprises twelvemetal rings 33 laminated one on another.

A forward drive gear 16 and a backward drive gear 17 are rotatablycarried on the driven shaft 10 and are capable of being selectivelycoupled to the driven shaft 10 by a selector 18. Secured to an outputshaft 19 disposed in parallel to the driven shaft 10 are a forwarddriven gear 20 meshed with the forward drive gear 16, and a backwarddriven gear 22 meshed with the backward drive gear 17 through a backwardidle gear 21.

The rotation of the output shaft 19 is inputted to a differential 25through a final drive gear 23 and a final driven gear 24 and thentransmitted from the differential 25 through left and right axles 26, 26to driven wheels W, W.

A driving force from the engine E is transmitted through the crankshaft1, the damper 2, the input shaft 3, the starting clutch 4, the driveshaft 5, the drive pulley 6, the metal belt 15 and the driven pulley 11to the driven shaft 10. When a forward travel range is selected, thedriving force of the driven shaft 10 is transmitted through the forwarddrive gear 16 and the forward driven gear 20 to the output shaft 19 tomove the vehicle forwards. When a backward travel range is selected, thedriving force of the driven shaft 10 is transmitted through the backwarddrive gear 17, the backward idle gear 21 and the backward driven gear 22to the output shaft 19 to move the vehicle backwards.

During this time, the shift ratio of the metal belt-type continuouslyvariable transmission T is continuously regulated by controlling thehydraulic pressures applied to the oil chamber 9 in the drive pulley 6and the oil chamber 14 in the driven pulley 11 of the transmission T bya hydraulic pressure control unit U₂ which is operated by a command froman electronic control unit U₁. More specifically, if the hydraulicpressure applied to the oil chamber 14 in the driven pulley 11 isincreased relative to the hydraulic pressure applied to the oil chamber9 in the drive pulley 6, a groove width of the driven pulley 11 isdecreased, leading to an increased effective radius. Attendant on this,a groove width of the drive pulley 6 is increased, leading to adecreased effective radius. Therefore, the shift ratio of the metalbelt-type continuously variable transmission T is varied continuouslytoward “LOW”. Reversely, if the hydraulic pressure applied to the oilchamber 9 in the drive pulley 6 is increased relative to the hydraulicpressure applied to the oil chamber 14 in the driven pulley 11, thegroove width of the drive pulley 6 is decreased, leading to an increasedeffective radius. Attendant on this, the groove width of the drivenpulley 11 is increased, leading to a decreased effective radius.Therefore, the shift ratio of the metal belt-type continuously variabletransmission T is varied continuously toward “OD”.

As shown in FIGS. 2 and 3, the metal element 32 formed from a metalplate by pressing and punching includes a substantially trapezoidalelement body 34, and a substantially triangular ear portion 36 connectedto an upper portion of the element body 34 through a pair of left andright ring slots 35, 35 into which the metal ring assemblies 31, 31 arefitted, respectively. A pair of pulley abutment surfaces 37, 37 areformed on left and right opposite edges of the element body 34 and arecapable of being brought into abutment against V-surfaces of the drivepulley 6 and the driven pulley 11. A pair of front and rear mainsurfaces 38 and 39 extending perpendicular to a direction of movement ofthe metal element 32 are formed on front and rear sides of the metalelement 32 in the direction of movement, and a slope 41 is formed belowthe main surface 38 which is on the front side in the direction ofmovement with a laterally extending rocking edge 40 interposedtherebetween. Further, a projection 42 and a recess 43 are formedrespectively on the main surface 38 on the front side in the directionof movement and the main surface 39 on the rear side in the direction ofmovement, which correspond to the ear portion 36.

Thus, adjacent ones of the metal elements 32 lying in an advancing-sidechord portion extending from the drive pulley 6 toward the driven pulley11 (i.e., a chord portion capable of transmitting a driving force)transmit the driving force between the elements in a state in which themain surfaces 38 on the front side and the main surface 39 on the rearside are in abutment against each other, and the projection 42 on thefront side has been fitted in the recess 43 on the rear side in theadjacent elements. The metal elements 32 wound around the drive pulley 6and the driven pulley 11 are swung relative to each other by releasingof the contact of the main surfaces 38 and 39 with each other, and arearranged radiately in radial directions of the pulleys 6 and 11.

The inclination of the metal element 32 in a pitching direction will beconsidered below with reference to FIG. 3. The metal element 32 has therocking edge 40 provided on a front surface in the direction of movementto permit the inclination of the metal element 32 in the pitchingdirection. The center 44 of swinging movement of the metal element 32actually causing the pitching is a widthwise central position of themetal element 32 at the rear of the rocking edge 40. This is because theinclination of the metal element 32 is limited with the ring slot 35fitted over the metal ring assembly 31 and hence, when the metal element32 is inclined, the inclination occurs about a position in which areaction force received from the metal ring assembly 31 is minimum,i.e., about the center 44 of swinging movement.

The tangential friction force acting on the metal element 32 is maximumand the urging force between the metal elements 32 is zero in an outletportion of the driven pulley 11, as described above. Therefore, themetal element 32 is liable to be inclined to the largest extent in theoutlet portion of the driven pulley.

FIG. 3 shows the balance of a force acting on the metal element 32having a thickness t in the outlet portion of the driven pulley 11. Atangential friction force FV acting on the metal element 32 from thedriven pulley 11 acts on a substantially central friction force-actingpoint 45 of the pulley abutment surface 37 of the metal element 32, andthe direction thereof is backward in the direction of movement toinhibit the movement of the metal element 32. If the radius or distanceof the center 44 of swinging movement about the axis of the drivenpulley 11 is represented by RL, and the radius of the frictionforce-acting point 45 about the axis of the driven pulley 11 isrepresented by RV, the distance L between the center 44 of swingingmovement and the friction force-acting point 45 is given by RL-RV.Therefore, a counterclockwise moment FV×L is applied to the metalelement 32 about the center 44 of swinging movement by the tangentialfriction force FV. This moment FV×L acts to fall the metal element 32forwards (in a direction to fall the radially outer end of the metalelement 32 forwards).

When the metal element 32 has been inclined forwards, a radially inwardload FL is applied from the metal ring assembly 31 to an edge a at arear end of the ring slot 35. The load FL generates a clockwise momentFL×(t/2) about the center 44 of swinging movement. Therefore, to preventthe inclination of the metal element 32 by the tangential friction forceFV, the following relation may be established:

FV×L≦FL×(t/2)  (1)

If this is solved for L/t, the following relation is given:

L/t≦FL/2FV  (2)

A graph in FIG. 5 shows a region in which the relation (2) isestablished (a region shown by oblique lines) with respect to variousinput torques of the metal belt-type continuously variable transmissionT. The conditions for the operation of the metal belt-type continuouslyvariable transmission T are an input rotational speed of 6000 rpm, aratio of 0.61 and a thickness t of the metal element 32 of 1.5 mm.

As can be seen from FIG. 5, the value of L/t is decreased with anincrease in input torque, and when the input torque reaches the maximumvalue of 14.3 kgf·m corresponding to the severest operational condition,FV=10.84 kgf and FL=22.66 kgf are established and hence, FL/2FV=1.05 isestablished. Thus, if the L/t is set at 1.05 or less in this embodiment,the relation (2) can be established even during the operation at thehighest speed which is the severest operational condition to prevent theinclination of the metal element 32.

As a result, it is possible to prevent a local load from being appliedbetween the edge a of the ring slot 35 and the inner periphery of themetal ring assembly 31, and to inhibit the increase in amplitude of astress inside the innermost metal ring 33, thereby enhancing thedurability of the metal ring assembly 31. Moreover, the pulley abutmentsurface 37 of the metal element 32 can be accurately brought intosurface contact with the drive pulley 6 or the driven pulley 11 to avoidthe generation of an abnormal wearing, and also the outer periphery ofthe metal ring assembly 31 can be prevented from interfering with theear portion 36 of the metal element 32. Thus, it is possible to preventan increase in amplitude of the stress of the outermost metal ring 33,and to prevent the local load of the innermost metal ring 33 from beingincreased by a reaction force from the interference. It is unnecessaryto provide a special shape in the thickness-wise direction to the saddlesurface of the ring slot 35 in the metal element 32 and hence, the metalelement 32 can be formed only by pressing, whereby the processing costfor the metal element is reduced.

FIGS. 8A and 8B show the shape of a conventional metal element 32. Inthis metal element 32, because L/t exceeds 1.0, the inclination of themetal element 32 caused by a tangential friction force FV cannot beprevented. In contrast, in the embodiment shown in FIGS. 6A and 6B, theradial dimension of the pulley abutment surface 37 corresponding to thatshown in FIGS. 8A and 8B is shortened, and the friction force-actingpoint 45 is displaced radially outwards, whereby the distance L isshortened to achieve L/t=1.0. In the shape of the metal element 32 shownin FIGS. 7A and 7B, the rocking edge 40 corresponding to that shown inFIGS. 8A and 8B is displaced radially inwards, whereby the distance L isshortened to achieve L/t=1.0.

Although the embodiments of the present invention have been described indetail, it will be understood that various modifications in design maybe made without departing from the subject matter of the presentinvention.

What is claimed is:
 1. A belt for a continuously variable transmission, comprising metal ring assemblies (31) each of which is comprised of a plurality of endless metal rings (33) laminated one on another, and a large number of metal elements (32) supported along said metal ring assemblies (31), said belt being wound around a drive pulley (6) and a driven pulley (11) to transmit a driving force, said metal element (32) comprising ring slots (35) into which said metal ring assemblies (31) are fitted, pulley abutment surfaces (37) provided radially inside said ring slots (35) to abut against said drive pulley (6) and said driven pulley (11), a rocking edge (40) which is provided at a radially inner end of a main surface (38) for transmitting an urging force between said metal elements (32) and which serves as a fulcrum for the pitching of said metal elements (32), characterized in that a relation, L/t≦FL/2FV is established, wherein FV represents a tangential friction force received by said pulley abutment surface (37) from said drive pulley (6) and said driven pulley (11); L represents a radial distance from a point (45) of action of said tangential friction force to the rocking edge (40) located radially outside said friction force-acting point (45); FL represents a radially inward load received by said metal element (32) from said metal ring assemblies (31); and t represents a thickness of said metal element (32). 